Heat pump apparatus and method of controlling heat pump apparatus

ABSTRACT

In a heat pump apparatus of an indirect type including a primary circuit on a heat source side and a secondary circuit on a load side, a refrigerant in the primary circuit is prevented from leaking through the secondary circuit. 
     An air-conditioning apparatus includes a leakage detecting device that detects leakage of the refrigerant circulated through a refrigerant circuit, serving as the primary circuit, from an intermediate heat exchanger into a water circuit, serving as the secondary circuit, and a controller that closes valves arranged on both sides of the intermediate heat exchanger in the water circuit to prevent water containing the refrigerant from flowing beyond the valves when the leakage detecting device detects the leakage.

TECHNICAL FIELD

The present invention relates to a technique for securing safety when arefrigerant leaks from a heat pump apparatus.

BACKGROUND ART

An air-conditioning apparatus (an example of a heat pump apparatus) hasbeen known which utilizes a refrigeration cycle technique using arefrigerant as a way of cooling, heating, or dehumidifying a room.

Fluorine compounds, such as R410A that is hydrofluorocarbon (HFC), arewidely used as refrigerants in air-conditioning apparatuses. Theserefrigerants, however, have a considerable impact on global warming. Interms of prevention of global warming, therefore, it is desirable to userefrigerants having a less impact on global warming. Accordingly, theuse of refrigerants having a less impact on global warming, such as R32that is HFC, R1234yf that is hydrofluoro-olefin (HFO), propane andisobutene that are hydrocarbons, has been proposed. Disadvantageously,all of these refrigerants are flammable, unlike the conventionalrefrigerants.

In an air-conditioning apparatus using a flammable refrigerant, therefrigerant may leak from a heat exchanger, a pipe, or the like includedin a refrigeration cycle and an explosive atmosphere may accordingly beproduced in a room. This may lead to an accident, such as fire.

Patent Literature 1 discloses an air-conditioning apparatus thataddresses the above-described problem. This air-conditioning apparatusis of an indirect type including a primary circuit through which aflammable refrigerant is circulated and a secondary circuit throughwhich a nonflammable heat medium is circulated. In the indirectair-conditioning apparatus, the heat medium circulated through thesecondary circuit is heated or cooled by the flammable refrigerantcirculated through the primary circuit, the flammable refrigerantcirculated through the primary circuit is not permitted to flow to aroom, and only the heat medium circulated through the secondary circuitis permitted to flow to the room. The indirect air-conditioningapparatus prevents the flammable refrigerant from flowing to the room,thus preventing the room from being in an explosive atmosphere.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Unexamined Patent Application    Publication No. 2009-150620

SUMMARY OF INVENTION Technical Problem

In a typical indirect air-conditioning apparatus, a plate heat exchangeror a double pipe heat exchanger is used as an intermediate heatexchanger that exchanges heat between the flammable refrigerantcirculated through the primary circuit and the heat medium circulatedthrough the secondary circuit. In this case, the intermediate heatexchanger may be damaged due to freezing or deterioration over time.Unfortunately, a passage in the primary circuit may communicate with apassage in the secondary circuit, thus allowing the flammablerefrigerant circulated through the primary circuit to mix with the heatmedium circulated through the secondary circuit.

Additionally, mixing of the flammable refrigerant and the heat mediummay cause a pressure in the secondary circuit to increase.Disadvantageously, the heat medium containing the flammable refrigerantmay leak into a room from a welded seam or joint of pipes included inthe secondary circuit.

A primary object of the present invention is to prevent a refrigerant ina primary circuit from leaking through a secondary circuit in a heatpump apparatus that uses an indirect system including the primarycircuit on a heat source side and the secondary circuit on a load side.

Solution to Problem

The present invention provides a heat pump apparatus including a firstrefrigerant circuit through which a refrigerant is circulated and thatincludes a first compressor, a first heat source heat exchanger, a firstexpansion mechanism, and a first intermediate heat exchangersequentially connected in loop by pipes, a fluid circuit through which afluid is circulated and that includes the first intermediate heatexchanger, a first valve, a load heat exchanger, and a second valvesequentially connected in loop by pipes, a leakage detecting device thatdetects leakage of the refrigerant, circulated through the firstrefrigerant circuit, from the first intermediate heat exchanger into thefluid circuit, and a controller that closes the first valve and thesecond valve included in the fluid circuit when the leakage detectingdevice detects the leakage of the refrigerant.

Advantageous Effects of Invention

The heat pump apparatus according to the present invention closes thefirst valve and the second valve when the refrigerant leaks from thefirst refrigerant circuit, serving as a primary circuit, into the fluidcircuit, serving as a secondary circuit, thus preventing the refrigerantcirculated through the primary circuit from flowing beyond the firstvalve and the second valve in the secondary circuit. Advantageously, therefrigerant circulated through the primary circuit can be prevented fromleaking beyond the first valve and the second valve in the secondarycircuit to the outside.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the configuration of anair-conditioning apparatus 100 according to Embodiment 1.

FIG. 2 is a diagram illustrating the flow of a refrigerant and the flowof water during a cooling operation in the air-conditioning apparatus100 according to Embodiment 1.

FIG. 3 is a diagram illustrating the flow of the refrigerant and theflow of the water during a heating operation in the air-conditioningapparatus 100 according to Embodiment 1.

FIG. 4 is a flowchart illustrating an operation of a leakage detectingdevice 13 and that of a controller 14 in Embodiment 1.

FIG. 5 is a diagram illustrating the configuration of anair-conditioning apparatus 100 according to Embodiment 2.

FIG. 6 is a diagram illustrating the flow of the refrigerant and theflow of the water during the cooling operation in the air-conditioningapparatus 100 according to Embodiment 2.

FIG. 7 is a diagram illustrating the flow of the refrigerant and theflow of the water during the heating operation in the air-conditioningapparatus 100 according to Embodiment 2.

FIG. 8 is an exploded perspective view of a typical plate heatexchanger.

FIG. 9 is a diagram illustrating arrangement of intermediate heatexchangers 5 a and 5 b according to Embodiment 3.

FIG. 10 is a diagram illustrating arrangement of the intermediate heatexchangers 5 a and 5 b according to Embodiment 3.

FIG. 11 is a diagram illustrating arrangement of the intermediate heatexchangers 5 a and 5 b according to Embodiment 3.

DESCRIPTION OF EMBODIMENTS Embodiment 1

FIG. 1 is a diagram illustrating the configuration of anair-conditioning apparatus 100 according to Embodiment 1. In FIG. 1,each blanked arrow indicates the flow of air and each dotted arrowindicates the flow of a signal.

The air-conditioning apparatus 100 includes a refrigerant circuit 6(first refrigerant circuit or primary circuit) that includes acompressor 1 (first compressor), a four-way valve 2, a heat exchanger 3(first heat exchanger), an expansion valve 4 (first expansionmechanism), an intermediate heat exchanger 5 (first intermediate heatexchanger) sequentially connected in loop by pipes. The air-conditioningapparatus 100 further includes a water circuit 10 (fluid circuit orsecondary circuit) that includes the intermediate heat exchanger 5, apump 7, a valve 8 a (first valve), a heat exchanger 9 (load heatexchanger), and a valve 8 b (second valve) sequentially connected inloop by pipes. A flammable refrigerant, such as a propane or isobutane,having a lower liquid density (liquid head) than water is circulatedthrough the refrigerant circuit 6 and water is circulated through thewater circuit 10. A fan 11 that delivers airflow to the heat exchanger 3is disposed near the heat exchanger 3. A fan 12 that delivers airflow tothe heat exchanger 9 is disposed near the heat exchanger 9.

The air-conditioning apparatus 100 further includes a leakage detectingdevice 13 that detects leakage of the refrigerant, circulated throughthe refrigerant circuit 6, from the intermediate heat exchanger 5 intothe water circuit 10 and a controller 14 that closes the valves 8 a and8 b when the leakage detecting device 13 detects the leakage of therefrigerant.

The compressor 1, the four-way valve 2, the heat exchanger 3, theexpansion valve 4, the intermediate heat exchanger 5, the pump 7, thevalves 8 a and 8 b, the fan 11, the leakage detecting device 13, and thecontroller 14 of the components included in the air-conditioningapparatus 100 are accommodated in an outdoor unit 15 (first casing)installed outside a room. The heat exchanger 9 and the fan 12 of thecomponents included in the air-conditioning apparatus 100 areaccommodated in an indoor unit 16 (second casing) installed inside theroom.

The intermediate heat exchanger 5 is a plate heat exchanger or doublepipe heat exchanger that has high efficiency of heat exchange. The pump7 is a pump having a variable rotation speed. The valve 8 a is a valvethat includes a variable expansion mechanism capable of controlling anopening degree. The valve 8 b is a valve that performs a simple openingand closing operation. The leakage detecting device 13 detects apressure in the water circuit 10 using a pressure sensor to detectleakage of the refrigerant. The leakage detecting device 13 detects, inparticular, a pressure at a point between the pump 7 and the valve 8 ato detect the leakage of the refrigerant. The controller 14 is amicrocomputer.

An operation of the air-conditioning apparatus 100 according toEmbodiment 1 during a cooling operation will be described.

FIG. 2 is a diagram illustrating the flow of the refrigerant and that ofthe water during the cooling operation in the air-conditioning apparatus100 according to Embodiment 1. In FIG. 2, solid line arrows indicate theflow of the refrigerant and broken line arrows indicate the flow of thewater.

During the cooling operation, the four-way valve 2 is set so as toprovide passages indicated by solid lines illustrated in FIG. 1. Anopening degree of the valve 8 a is set in such a manner that the waterflows at a constant rate. The valve 8 b is opened. Controlling the flowrate of the water flowing through the valve 8 a controls the amount ofheat exchange in the heat exchanger 9.

In the refrigerant circuit 6, a high-temperature high-pressurerefrigerant, obtained by the compressor 1, passes through the four-wayvalve 2 and flows into the heat exchanger 3. The refrigerant, which hasflowed into the heat exchanger 3, exchanges heat with outdoor air, sothat the refrigerant condenses into a liquid refrigerant. The liquidrefrigerant passes through the expansion valve 4 where the refrigerantis expanded into a low-temperature, low-pressure two-phase gas-liquidrefrigerant. The two-phase gas-liquid refrigerant flows into theintermediate heat exchanger 5 and exchanges heat with the watercirculated through the water circuit 10, so that the refrigerantevaporates into a gas refrigerant. At this time, the water circulatedthrough the water circuit 10 is cooled. The gas refrigerant passesthrough the four-way valve 2 and is sucked into the compressor 1, wherethe refrigerant is compressed into a high-temperature high-pressurestate.

On the other hand, in the water circuit 10, low temperature water,obtained by cooling through the intermediate heat exchanger 5, passesthrough the pump 7 and the valve 8 a in sequence and then flows into theheat exchanger 9. The water, which has flowed into the heat exchanger 9,exchanges heat with indoor air, so that the water is heated. At thistime, the indoor air is cooled. The heated water passes through thevalve 8 b and then flows into the intermediate heat exchanger 5.

An operation of the air-conditioning apparatus 100 according toEmbodiment 1 during a heating operation will be described.

FIG. 3 is a diagram illustrating the flow of the refrigerant and that ofthe water during the heating operation in the air-conditioning apparatus100 according to Embodiment 1. In FIG. 3, solid line arrows indicate theflow of the refrigerant and broken line arrows indicate the flow of thewater.

During the heating operation, the four-way valve 2 is set so as toprovide passages indicated by broken lines illustrated in FIG. 1. Theopening degree of the valve 8 a is set in such a manner that the flowrate of the water reaches a predetermined value. The valve 8 b isopened.

In the refrigerant circuit 6, a high-temperature high-pressurerefrigerant, obtained by the compressor 1, passes through the four-wayvalve 2 and flows into the intermediate heat exchanger 5. Therefrigerant, which has flowed into the intermediate heat exchanger 5,exchanges heat with the water circulated through the water circuit 10,so that the refrigerant condenses into a liquid refrigerant. At thistime, the water circulated through the water circuit 10 is heated. Theliquid refrigerant passes through the expansion valve 4, where therefrigerant is expanded into a low-temperature, low-pressure two-phasegas-liquid refrigerant. The two-phase gas-liquid refrigerant flows intothe heat exchanger 3 and exchanges heat with the outdoor air, so thatthe refrigerant evaporates into a gas refrigerant. The gas refrigerantpasses through the four-way valve 2 and is sucked into the compressor 1,where the refrigerant is compressed into a high-temperaturehigh-pressure state.

On the other hand, in the water circuit 10, high temperature water,obtained by heating through the intermediate heat exchanger 5, passesthrough the pump 7 and the valve 8 a in sequence and then flows into theheat exchanger 9. The water, which has flowed into the heat exchanger 9,exchanges heat with the indoor air, so that the water is cooled. At thistime, the indoor air is heated. The cooled water passes through thevalve 8 b and then flows into the intermediate heat exchanger 5.

An operation of the air-conditioning apparatus 100 according toEmbodiment 1 during a defrosting operation will be described.

The defrosting operation is performed when the heat exchanger 3 iscovered with frost during the heating operation.

The operation during the defrosting operation is the same as that duringthe cooling operation. Specifically, as illustrated in FIG. 2, thefour-way valve 2 is set so as to provide the passages indicated by thesolid lines illustrated in FIG. 1. In the refrigerant circuit 6, thehigh-temperature high-pressure refrigerant, obtained by the compressor1, passes through the four-way valve 2 and then flows into the heatexchanger 3. The frost on the heat exchanger 3 is melted by thehigh-temperature high-pressure refrigerant, which has flowed into theheat exchanger 3, and is then removed. Since the rest of the operationis the same as that during the cooling operation, description thereforis omitted.

As described above, during the cooling operation or the defrostingoperation, the low temperature refrigerant flows into the intermediateheat exchanger 5. The refrigerant at or below 0 degrees C. may flow intothe intermediate heat exchanger 5. In this case, the water circulatedthrough the water circuit 10 may freeze in the intermediate heatexchanger 5. An increase in volume of water upon freezing may cause theintermediate heat exchanger 5 to be damaged. If the intermediate heatexchanger 5 is damaged, a refrigerant passage in the intermediate heatexchanger 5 may communicate with a water passage therein, thus causingthe refrigerant circulated through the refrigerant circuit 6 to leakinto the water circuit 10. Furthermore, the intermediate heat exchanger5 may be damaged due to deterioration over time or the like, thuscausing the refrigerant circulated through the refrigerant circuit 6 toleak into the water circuit 10.

In case of leakage of the refrigerant into the water circuit 10, therefrigerant would mix with the water and the mixture would be circulatedthrough the water circuit 10. When a high pressure refrigerant mixeswith water, a refrigerant gas is produced by the effect of pressurereduction. Accordingly, a pressure in the water circuit 10 may exceed awithstanding pressure of, for example, pipes included in the watercircuit 10 or welded part of the pipes, thus causing the watercontaining the refrigerant to leak into the room.

An operation of the air-conditioning apparatus 100 according toEmbodiment 1 upon leakage of the refrigerant from the intermediate heatexchanger 5 into the water circuit 10 will be described.

FIG. 4 is a flowchart illustrating an operation of the leakage detectingdevice 13 and that of the controller 14 in Embodiment 1.

The leakage detecting device 13 detects a pressure in the water circuit10 at all times (S1: pressure detecting step) and determines whether thepressure in the water circuit 10 has increased (S2: increase determiningstep). When determining that the pressure has increased (YES in S2), theleakage detecting device 13 determines that the refrigerant has leakedinto the water circuit 10 and transmits a detection signal indicatingthe leakage of the refrigerant to the controller 14 (S3: signaltransmitting step). The controller 14 closes the valves 8 a and 8 b inresponse to reception of detection signal (S4: valve control step).Closing the valves 8 a and 8 b can prevent the water containing therefrigerant from flowing into the indoor unit 16.

In S2, depending on the situation, namely, while the air-conditioningapparatus 100 is stopped, alternatively, while the air-conditioningapparatus 100 is operating, the leakage detecting device 13 determinesthe increase of the pressure as follows.

While the air-conditioning apparatus 100 is stopped, the pressure in thewater circuit 10 is atmospheric pressure. Accordingly, a threshold valueto be used during stop of the air-conditioning apparatus 100 is set to apressure that is higher than the atmospheric pressure by a predeterminedvalue. When detecting a pressure higher than the threshold value, theleakage detecting device 13 determines that the pressure has increased.

While the air-conditioning apparatus 100 is operating, the pressure inthe water circuit 10 is higher than that detected during stop of theair-conditioning apparatus 100 because the water is circulated. The rateof the water circulated varies depending on, for example, the rotationspeed of the pump 7, so that the pressure in the water circuit 10 alsovaries. Accordingly, a value that is higher than a maximum pressure,which may be measured so long as the refrigerant does not leak, in thewater circuit 10 by a given value is determined as a threshold value inadvance. When detecting a pressure higher than the threshold value, theleakage detecting device 13 determines that the pressure has increased.The threshold values may be determined when the air-conditioningapparatus 100 is designed, for example. Alternatively, upon installationof the air-conditioning apparatus 100 in situ, operation simulation maybe performed in consideration of actual conditions, such as the lengthsof arranged pipes and the amount of refrigerant enclosed, and thethreshold values may be determined on the basis of the simulation.Alternatively, a threshold value may be determined in association with,for example, each of the rotation speed of the pump 7, an indoor airtemperature, and an outdoor air temperature. The leakage detectingdevice 13 may change a threshold value to be used depending on therotation speed of the pump 7, the indoor air temperature, or the outdoorair temperature upon pressure detection.

In case of leakage of the refrigerant, a pressure increases in theentire water circuit 10 in principle. If the opening degree of the valve8 a is controlled in such a manner that the flow rate of the watercirculated through the water circuit 10 is constant, however, the watercontaining a gas refrigerant is in a two-phase gas-liquid state.Accordingly, the difference between a pressure at a point prior to thevalve 8 a and a pressure at a point after the valve 8 a may increase anda pressure at a point downstream of the valve 8 a may be kept low, orincrease very little. The leakage detecting device 13 therefore detectsa pressure at a point between the pump 7 and the valve 8 a in the watercircuit 10. Consequently, an increase in pressure can be reliablydetected, irrespective of the opening degree of the valve 8 a.

As described above, the air-conditioning apparatus 100 according toEmbodiment 1 detects the leakage of the refrigerant circulated throughthe refrigerant circuit 6 into the water circuit 10 and closes thevalves 8 a and 8 b. Thus, the water containing the refrigerant can beprevented from flowing into the indoor unit 16. Consequently, theleakage of the refrigerant into the room can be prevented, thuspreventing the room from being in an explosive atmosphere.

In the above description, the controller 14 closes the valves 8 a and 8b in response to reception of detection signal. When receiving thedetection signal during operation of the air-conditioning apparatus 100,the controller 14 may close the valves 8 a and 8 b and stop thecompressor 1 or the pump 7. Consequently, the leakage of the refrigerantcan be prevented more reliably.

Furthermore, the controller 14 may prompt a user to ventilate the roomupon receiving the detection signal. For example, the controller 14 mayallow a remote control, which is used to enter an instruction for theindoor unit 16 or the air-conditioning apparatus 100, to output an audiomessage in order to prompt the user to ventilate the room. Thecontroller 14 may allow a display of the indoor unit 16 or the remotecontrol to display a message in order to prompt the user to ventilatethe room.

In the above description, the leakage detecting device 13 detects apressure in the water circuit 10 to detect the leakage of therefrigerant. The leakage detecting device 13 may detect the leakage ofthe refrigerant by any other method.

For example, the leakage detecting device 13 that detects the leakage ofthe refrigerant may be of, for example, a semiconductor type thatutilizes a reduction in electrical resistance of a semiconductor causedby adsorption of a gas on the surface of the semiconductor, a contactburning type that utilizes an increase in electrical resistance of aplatinum wire, through which current flows, caused by slight burning dueto contact between the platinum wire and a gas, or a gas thermalconductivity type that utilizes a change in temperature of a platinumwire, through which current flows, (typically in contact with air)caused by contact between the platinum wire and a flammable gas becausethe thermal conductivity of the air differs from that of the gas. Notethat a change in temperature of the platinum wire in the gas thermalconductivity type means a change in electrical resistance.

The above-described types use methods of detecting a flammable gas in anonflammable gas (e.g., air). An additional mechanism is thereforeneeded which allows the water circuit 10 to discharge a certain amountof water (or the mixture of the water and the refrigerant if therefrigerant has leaked) into the atmosphere at regular time intervalsand detects the refrigerant using any of the above methods after removalof the water. For example, when a pressure in the water circuit 10 is ator above a given pressure, the certain amount of water may be dischargedfrom the water circuit 10 into the atmosphere using a relief valve thatis opened when the pressure is at or above the given pressure.

To detect the leakage of the refrigerant using any of these methods, therelief valve may be disposed at the highest position in the watercircuit 10 and the leakage of the refrigerant may be detected from thedischarged mixture. A low density flammable refrigerant tends toaccumulate at the highest position in the water circuit 10. Accordingly,the leakage of the refrigerant can be reliably detected, irrespective ofduring operation or non-operation.

Embodiment 2

Embodiment 2 will be described with respect to an air-conditioningapparatus 100 including a plurality of primary circuits. Although theair-conditioning apparatus 100 including two primary circuits will bedescribed below as an example, the air-conditioning apparatus 100 mayinclude three or more primary circuits.

In the air-conditioning apparatus 100 according to Embodiment 2, thesame components as those in the air-conditioning apparatus 100 accordingto Embodiment 1 are designated by the same reference numerals.

FIG. 5 is a diagram illustrating the configuration of theair-conditioning apparatus 100 according to Embodiment 2. In FIG. 1,each blanked arrow indicates the flow of air and each dotted arrowindicates the flow of a signal.

The air-conditioning apparatus 100 includes a refrigerant circuit 6 a(first refrigerant circuit or primary circuit) including a compressor 1a (first compressor), a four-way valve 2 a, a heat exchanger 3 a (firstheat exchanger), an expansion valve 4 a (first expansion mechanism), anintermediate heat exchanger 5 a (first intermediate heat exchanger)sequentially connected in loop by pipes. The air-conditioning apparatus100 further includes a refrigerant circuit 6 b (second refrigerantcircuit or primary circuit) including a compressor 1 b (secondcompressor), a four-way valve 2 b, a heat exchanger 3 b (second heatexchanger), an expansion valve 4 b (second expansion mechanism), anintermediate heat exchanger 5 b (second intermediate heat exchanger)sequentially connected in loop by pipes. The air-conditioning apparatus100 further includes a water circuit 10 (fluid circuit or secondarycircuit) including the intermediate heat exchanger 5 a, the intermediateheat exchanger 5 b, a pump 7, a valve 8 a (first valve), a heatexchanger 9 (load heat exchanger), and a valve 8 b (second valve)sequentially connected in loop by pipes. A flammable refrigerant, suchas a propane or isobutane, having a lower liquid density than water iscirculated through each of the refrigerant circuits 6 a and 6 b, andwater is circulated through the water circuit 10. A fan 11 that deliversairflow to the heat exchangers 3 a and 3 b is disposed near the heatexchangers 3 a and 3 b. A fan 12 that delivers airflow to the heatexchanger 9 is disposed near the heat exchanger 9.

The air-conditioning apparatus 100 further includes a leakage detectingdevice 13 that detects leakage of the refrigerant, circulated throughthe refrigerant circuits 6, into the water circuit 10 from any of theintermediate heat exchangers 5 and a controller 14 that closes thevalves 8 a and 8 b when the leakage detecting device 13 detects theleakage of the refrigerant.

The compressors 1 a and 1 b, the four-way valves 2 a and 2 b, the heatexchangers 3 a and 3 b, the expansion valves 4 a and 4 b, theintermediate heat exchangers 5 a and 5 b, the pump 7, the valves 8 a and8 b, the fan 11, the leakage detecting device 13, and the controller 14of the components included in the air-conditioning apparatus 100 areaccommodated in an outdoor unit 15 (first casing). The heat exchanger 9and the fan 12 of the components included in the air-conditioningapparatus 100 are accommodated in an indoor unit 16 (second casing).

Each of the intermediate heat exchangers 5 a and 5 b is a plate heatexchanger or double pipe heat exchanger that has high efficiency of heatexchange.

An operation of the air-conditioning apparatus 100 according toEmbodiment 2 during the cooling operation will be described.

FIG. 6 is a diagram illustrating the flow of the refrigerant and that ofthe water during the cooling operation in the air-conditioning apparatus100 according to Embodiment 2. In FIG. 6, solid line arrows indicate theflow of the refrigerant and broken line arrows indicate the flow of thewater.

During the cooling operation, the four-way valves 2 a and 2 b are set soas to provide passages indicated by solid lines illustrated in FIG. 5.An opening degree of the valve 8 a is set in such a manner that thewater flows at a constant rate. The valve 8 b is opened.

In the refrigerant circuit 6 a, a high-temperature high-pressurerefrigerant, obtained by the compressor 1 a, passes through the four-wayvalve 2 a and flows into the heat exchanger 3 a. The refrigerant, whichhas flowed into the heat exchanger 3 a, exchanges heat with outdoor air,so that the refrigerant condenses into a liquid refrigerant. The liquidrefrigerant passes through the expansion valve 4 a, where therefrigerant is expanded into a low-temperature, low-pressure two-phasegas-liquid refrigerant. The two-phase gas-liquid refrigerant flows intothe intermediate heat exchanger 5 a and exchanges heat with the watercirculated through the water circuit 10, so that the refrigerantevaporates into a gas refrigerant. At this time, the water circulatedthrough the water circuit 10 is cooled. The gas refrigerant passesthrough the four-way valve 2 a and is sucked into the compressor 1 a,where the refrigerant is compressed into a high-temperaturehigh-pressure state.

As in the refrigerant circuit 6 a, in the refrigerant circuit 6 b, ahigh-temperature high-pressure refrigerant, obtained by the compressor 1b, passes through the four-way valve 2 b and flows into the heatexchanger 3 b. The refrigerant, which has flowed into the heat exchanger3 b, exchanges heat with the outdoor air, so that the refrigerantcondenses into a liquid refrigerant. The liquid refrigerant passesthrough the expansion valve 4 b, where the refrigerant is expanded intoa low-temperature, low-pressure two-phase gas-liquid refrigerant. Thetwo-phase gas-liquid refrigerant flows into the intermediate heatexchanger 5 b and exchanges heat with the water circulated through thewater circuit 10, so that the refrigerant evaporates into a gasrefrigerant. At this time, the water circulated through the watercircuit 10 is cooled. The gas refrigerant passes through the four-wayvalve 2 b and is sucked into the compressor 1 b, where the refrigerantis compressed into a high-temperature high-pressure state.

On the other hand, in the water circuit 10, the water is cooled in theintermediate heat exchanger 5 a and is further cooled to a lowtemperature in the intermediate heat exchanger 5 b. The low temperaturewater passes through the pump 7 and the valve 8 a in sequence and thenflows into the heat exchanger 9. The water, which has flowed into theheat exchanger 9, exchanges heat with indoor air, so that the water isheated. At this time, the indoor air is cooled. The heated water passesthrough the valve 8 b and then flows into the intermediate heatexchanger 5 a.

Since the intermediate heat exchangers 5 a and 5 b are connected inseries in the water circuit 10 as described above, the water issuccessively cooled by the refrigerant circulated through therefrigerant circuit 6 a and the refrigerant circulated through therefrigerant circuit 6 b. Accordingly, the water can be adequately cooledif the capacity of each of the refrigerant circuits 6 a and 6 b is nothigh.

An operation of the air-conditioning apparatus 100 according toEmbodiment 2 during the heating operation will be described.

FIG. 7 is a diagram illustrating the flow of the refrigerant and that ofthe water during the heating operation in the air-conditioning apparatus100 according to Embodiment 2. In FIG. 7, solid line arrows indicate theflow of the refrigerant and broken line arrows indicate the flow of thewater.

During the heating operation, the four-way valves 2 a and 2 b are set soas to provide passages indicated by broken lines illustrated in FIG. 5.The opening degree of the valve 8 a is set in such a manner that theflow rate of the water reaches a predetermined value. The valve 8 b isopened.

In the refrigerant circuit 6 a, a high-temperature high-pressurerefrigerant, obtained by the compressor 1 a, passes through the four-wayvalve 2 a and flows into the intermediate heat exchanger 5 a. Therefrigerant, which has flowed into the intermediate heat exchanger 5 a,exchanges heat with the water circulated through the water circuit 10,so that the refrigerant condenses into a liquid refrigerant. At thistime, the water circulated through the water circuit 10 is heated. Theliquid refrigerant passes through the expansion valve 4 a, where therefrigerant is expanded into a low-temperature, low-pressure two-phasegas-liquid refrigerant. The two-phase gas-liquid refrigerant flows intothe heat exchanger 3 a and exchanges heat with the outdoor air, so thatthe refrigerant evaporates into a gas refrigerant. The gas refrigerantpasses through the four-way valve 2 a and is sucked into the compressor1 a, where the refrigerant is compressed into a high-temperaturehigh-pressure state.

As in the refrigerant circuit 6 a, in the refrigerant circuit 6 b, ahigh-temperature high-pressure refrigerant, obtained by the compressor 1b, passes through the four-way valve 2 b and flows into the intermediateheat exchanger 5 b. The refrigerant, which has flowed into theintermediate heat exchanger 5 b, exchanges heat with the watercirculated through the water circuit 10, so that the refrigerantcondenses into a liquid refrigerant. At this time, the water circulatedthrough the water circuit 10 is heated. The liquid refrigerant passesthrough the expansion valve 4 b, where the refrigerant is expanded intoa low-temperature, low-pressure two-phase gas-liquid refrigerant. Thetwo-phase gas-liquid refrigerant flows into the heat exchanger 3 b andexchanges heat with the outdoor air, so that the refrigerant evaporatesinto a gas refrigerant. The gas refrigerant passes through the four-wayvalve 2 b and is sucked into the compressor 1 b, where the refrigerantis compressed into a high-temperature high-pressure state.

On the other hand, in the water circuit 10, the water is heated in theintermediate heat exchanger 5 a and is further heated to a hightemperature in the intermediate heat exchanger 5 b. The high temperaturewater passes through the pump 7 and the valve 8 a in sequence and thenflows into the heat exchanger 9. The water, which has flowed into theheat exchanger 9, exchanges heat with the indoor air, so that the wateris cooled. At this time, the indoor air is heated. The cooled waterpasses through the valve 8 b and then flows into the intermediate heatexchanger 5 a.

Since the intermediate heat exchangers 5 a and 5 b are connected inseries in the water circuit 10 as described above, the water issuccessively heated by the refrigerant circulated through therefrigerant circuit 6 a and the refrigerant circulated through therefrigerant circuit 6 b. Accordingly, the water can be adequately heatedif the capacity of each of the refrigerant circuits 6 a and 6 b is nothigh.

An operation of the air-conditioning apparatus 100 according toEmbodiment 2 during the defrosting operation will be described.

The defrosting operation is performed when the heat exchangers 3 a and 3b are covered with frost during the heating operation.

The operation during the defrosting operation is the same as that duringthe cooling operation. Specifically, as illustrated in FIG. 6, thefour-way valves 2 a and 2 b are set so as to provide the passagesindicated by the solid lines illustrated in FIG. 5. In the refrigerantcircuit 6 a, the high-temperature high-pressure refrigerant, obtained bythe compressor 1 a, passes through the four-way valve 2 a and flows intothe heat exchanger 3 a. Similarly, in the refrigerant circuit 6 b, thehigh-temperature high-pressure refrigerant, obtained by the compressor 1b, passes through the four-way valve 2 b and flows into the heatexchanger 3 b. The frost on the heat exchangers 3 a and 3 b is melted bythe high-temperature high-pressure refrigerant which has flowed into theheat exchangers 3 a and 3 b and is then removed. Since the rest of theoperation is the same as that during the cooling operation, descriptionis omitted.

As in the air-conditioning apparatus 100 according to Embodiment 1, inthe air-conditioning apparatus 100 according to Embodiment 2, theintermediate heat exchangers 5 a and 5 b may be damaged and therefrigerant circulated through the refrigerant circuits 6 may leak intothe water circuit 10. If the refrigerant leaks into the water circuit10, the water containing the refrigerant may leak into a room.

When the leakage of the refrigerant circulated through the refrigerantcircuits 6 into the water circuit 10 is detected, the controller 14closes the valves 8 a and 8 b. This prevents the leakage of the watercontaining the refrigerant from flowing into the indoor unit 16. Inaddition, the controller 14 may stop the compressors 1 a and 1 b or thepump 7 to reliably prevent the leakage of the refrigerant.

As described above, like the air-conditioning apparatus 100 according toEmbodiment 1, the air-conditioning apparatus 100 according to Embodiment2 detects the leakage of the refrigerant circulated through therefrigerant circuits 6 a and 6 b into the water circuit 10 and closesthe valves 8 a and 8 b. Thus, the water containing the refrigerant canbe prevented from flowing into the indoor unit 16. Consequently, theleakage of the refrigerant into the room can be prevented, thuspreventing the room from being in an explosive atmosphere.

Furthermore, it is preferred that the amount of refrigerant enclosed ineach primary circuit be below a predetermined amount (for example, 150g, based on the F-gas Regulation in Europe, in the use of propane as arefrigerant, for example) so that a room is prevented from being in anexplosive atmosphere if the refrigerant leaks into the room. Typically,however, a large amount of refrigerant is enclosed in a largeair-conditioning apparatus having a high capacity.

In the air-conditioning apparatus 100 according to Embodiment 2including the two primary circuits, namely, the refrigerant circuits 6 aand 6 b, if the refrigerant enclosed in each of the refrigerant circuits6 a and 6 b is restricted to a small amount and the capacity of each ofthe refrigerant circuits 6 a and 6 b is accordingly low, theair-conditioning apparatus 100 can demonstrate a high capacity. In otherwords, if the air-conditioning apparatus 100 according to Embodiment 2is a large air-conditioning apparatus that demonstrates a high capacity,the amount of refrigerant enclosed in each primary circuit can be small.

Furthermore, as illustrated in FIG. 5, the airflow delivered by the fan11 passes through the heat exchanger 3 a and then passes through theheat exchanger 3 b. For example, during the cooling operation,therefore, the heat exchanger 3 a exchanges heat between the air and therefrigerant circulated through the refrigerant circuit 6 a and theheated air is delivered to the heat exchanger 3 b. In other words, thetemperature of the airflow supplied to the heat exchanger 3 a differsfrom that of the airflow supplied to the heat exchanger 3 b.Consequently, a condensing temperature in the refrigerant circuit 6 acan be allowed to differ from that in the refrigerant circuit 6 b.

In addition, as illustrated in FIG. 5, the water circulated through thewater circuit 10 passes through the intermediate heat exchanger 5 a andthen passes through the intermediate heat exchanger 5 b. For example,during the cooling operation, therefore, the intermediate heat exchanger5 a exchanges heat between the water and the refrigerant circulatedthrough the refrigerant circuit 6 a and the cooled water is delivered tothe intermediate heat exchanger 5 b. In other words, the temperature ofthe water supplied to the intermediate heat exchanger 5 a differs fromthat of the water supplied to the intermediate heat exchanger 5 b.Consequently, an evaporating temperature in the refrigerant circuit 6 acan be allowed to differ from that in the refrigerant circuit 6 b.

In other words, the condensing temperature and the evaporatingtemperature in the refrigerant circuit 6 a can be allowed to differ fromthose in the refrigerant circuit 6 b. Although the above description hasbeen made with respect to the cooling operation, the condensingtemperature and the evaporating temperature in the refrigerant circuit 6a during the heating operation can similarly be allowed to differ fromthose in the refrigerant circuit 6 b. Since the condensing temperatureand the evaporating temperature in the refrigerant circuit 6 a areallowed to differ from those in the refrigerant circuit 6 b, thetemperature of the refrigerant is allowed to change depending on thetemperature of water or air, thus enabling the air-conditioningapparatus to achieve high efficiency.

In the case illustrated in FIG. 5, during the cooling operation, the airheated by heat exchange through the heat exchanger 3 a is delivered tothe heat exchanger 3 b, so that the condensing temperature in the heatexchanger 3 a is low and the condensing temperature in the heatexchanger 3 b is high. In addition, the water cooled by heat exchangethrough the intermediate heat exchanger 5 a flows into the intermediateheat exchanger 5 b, so that the evaporating temperature in theintermediate heat exchanger 5 a is high and the evaporating temperaturein the intermediate heat exchanger 5 b is low. During the heatingoperation, the air cooled by heat exchange through the heat exchanger 3a is delivered to the heat exchanger 3 b, so that the evaporatingtemperature in the heat exchanger 3 a is high and the evaporatingtemperature in the heat exchanger 3 b is low. In addition, the waterheated by heat exchange through the intermediate heat exchanger 5 aflows into the intermediate heat exchanger 5 b, so that the condensingtemperature in the intermediate heat exchanger 5 a is low and thecondensing temperature in the intermediate heat exchanger 5 b is high.

Specifically, in the case illustrated in FIG. 5, the refrigerant circuit6 a is a circuit in which the condensing temperature is low and theevaporating temperature is high and the refrigerant circuit 6 b is acircuit in which the condensing temperature is high and the evaporatingtemperature is low. Accordingly, the difference between a high pressureand a low pressure is reduced in the refrigerant circuit 6 a and thedifference therebetween is increased in the refrigerant circuit 6 b.

The difference in high-low pressure difference between the refrigerantcircuit 6 a and the refrigerant circuit 6 b may be reduced by allowingthe airflow generated by the fan 11 to pass through the heat exchanger 3b and then pass through the heat exchanger 3 a, or allowing the watercirculated through the water circuit 10 to pass through the intermediateheat exchanger 5 b and then pass through the intermediate heat exchanger5 a.

As regards increasing or decreasing the difference in high-low pressuredifference between the refrigerant circuits 6 a and 6 b, the increase orthe decrease may be selected depending on the difference in performancebetween the compressors included in the refrigerant circuits 6 a and 6b, an installation environment of the air-conditioning apparatus 100, orthe like so that high efficiency is achieved.

Embodiment 3

Embodiment 3 will be described with respect to placement of theintermediate heat exchanger 5 (5 a, 5 b) in Embodiments 1 and 2. Theplacement will be described with respect to the air-conditioningapparatus 100 according to Embodiment 2 as an example.

FIG. 8 is an exploded perspective view of a typical plate heatexchanger.

FIGS. 9 to 11 are diagrams illustrating arrangement of the intermediateheat exchangers 5 a and 5 b according to Embodiment 3. In FIGS. 9 to 11,solid line arrows indicate the flow of refrigerant during the coolingoperation and broken line arrows indicate the flow of water. During theheating operation, the refrigerant flows in a direction opposite to thatindicated by the solid line arrows. In FIGS. 9 to 11, an up-downdirection corresponds to a vertical direction.

In FIGS. 9 to 11, it is assumed that each of the intermediate heatexchangers 5 a and 5 b is a plate heat exchanger. As illustrated in FIG.8, the plate heat exchanger includes a plurality of substantiallyrectangular plates 51 arranged and has a thin rectangular-parallelepipedshape in appearance. The plate 51 at one end of the stacked plates 51has connection ports 52 and 53 for the primary circuit and connectionports 54 and 55 for the secondary circuit. Refrigerant passages 56through which the refrigerant circulated through the primary circuitflows and water passages 57 through which the water circulated throughthe secondary circuit flows are alternately arranged between theadjacent plates.

In FIG. 9, the two rectangular-parallelepiped intermediate heatexchangers 5 a and 5 b are vertically stacked. To accommodate the tworefrigerant circuits 6 a and 6 b, the outdoor unit 15 is increased insize and the area of installation of the outdoor unit 15 is alsoincreased. Since the two intermediate heat exchangers 5 a and 5 b arevertically stacked as illustrated in FIG. 9, however, the intermediateheat exchangers 5 a and 5 b can be arranged with efficiency. Thus, theinstallation area of the outdoor unit 15 can be reduced.

Note that connection ports 53 a and 53 b adjacent to the expansionvalves 4 a and 4 b and connection ports 55 a and 55 b adjacent to thepump 7 are arranged on a lower side and connection ports 52 a and 52 badjacent to the four-way valves 2 a and 2 b and connection ports 54 aand 54 b adjacent to the valve 8 b are arranged on an upper side. Duringthe cooling operation and the defrosting operation, the two-phaserefrigerant enters through the connection ports 53 a and 53 b and thegas refrigerant leaves through the connection ports 52 a and 52 b.During the heating operation, the gas refrigerant enters through theconnection ports 52 a and 52 b and the liquid refrigerant leaves throughthe connection ports 53 a and 53 b. In this arrangement in which theconnection ports 52 a and 52 b through which the gas refrigerant passesare arranged on the upper side, therefore, accumulation of the gasrefrigerant in the intermediate heat exchangers 5 a and 5 b can beprevented.

Referring to FIGS. 10 and 11, the intermediate heat exchangers 5 a and 5b are inclined in such a manner that the connection ports 52 a, 52 b, 54a, and 54 b face obliquely upward. In this arrangement, whereas the areaof installation of the outdoor unit 15 is slightly increased, the areaof accumulation of the gas refrigerant in an upper portion (area 58 a or58 b indicated by a broken line in FIG. 9) of each of the intermediateheat exchangers 5 a and 5 b can be reduced.

In FIG. 11 which illustrates a modification of the configuration of FIG.10, the connection ports 52 a, 52 b, 54 a, and 54 b are arranged at oneends and the connection ports 53 a, 53 b, 55 a, and 55 b are provided inthe plates 51 arranged at the another ends, respectively. The connectionports 53 a and 53 b are inlets for the refrigerant during the coolingoperation and the defrosting operation.

In case of leakage of a small amount of refrigerant, the refrigerant gasmay accumulate in the intermediate heat exchangers 5 a and 5 b anddetection of the leakage of the refrigerant may accordingly be delayed.The above-described arrangement manner, however, can reduce the areaswhere the refrigerant gas accumulates in the intermediate heatexchangers 5 a and 5 b. Consequently, the leakage of the refrigerant canbe immediately detected.

The intermediate heat exchangers 5 a and 5 b in Embodiment 2 have beendescribed above as an example. As regards the air-conditioning apparatus100 according to Embodiment 1, the intermediate heat exchanger 5 may beplaced vertically as illustrated in FIG. 9. Alternatively, theintermediate heat exchanger 5 may be inclined as illustrated in FIG. 10.The connection ports may be provided in the plates 51 arranged at theanother ends as illustrated in FIG. 11.

In a configuration in which at least two primary refrigerant circuitsare arranged and R32, HFO-1234yf, a refrigerant mixture containing R32,or a refrigerant mixture containing HFO-1234yf having a higher liquiddensity (liquid head) than water is used as a flammable refrigerantcirculated through each primary refrigerant circuit, each intermediateheat exchanger is vertically placed and the intermediate heat exchangersare arranged side by side horizontally. Specifically, the intermediateheat exchangers 5 a and 5 b are arranged side by side horizontally in astate in which the connection ports 53 a, 53 b, 55 a, and 55 b arearranged on the lower side and the connection ports 52 a, 52 b, 54 a,and 54 b are arranged on the upper side. Consequently, the performancecan be ensured and an upper space within the outdoor unit 15 can be usedas a refrigerant pipe space, so that the area of installation can bereduced.

In Embodiments 1, 2 and 3 the water is circulated through the watercircuit 10 which serves as the secondary circuit. The fluid circulatedthrough the secondary circuit is not limited to water. Any othernonflammable fluid, such as brine, may be used.

If brine is circulated through the secondary circuit; the brine wouldnot freeze in the intermediate heat exchanger 5 (or the intermediateheat exchangers 5 a and 5 b in Embodiment 2). The intermediate heatexchanger 5, however, may be damaged due to deterioration over time orthe like. The air-conditioning apparatus 100 according to each ofEmbodiments 1 and 2 is effective in the case where brine is circulatedthrough the secondary circuit.

In Embodiments 1 and 2, the pump 7 is disposed between the intermediateheat exchanger 5 (the intermediate heat exchanger 5 b in Embodiment 2)and the valve 8 a in the water circuit 10. The pump 7 may be disposed atany other position between the valves 8 a and 8 b in a direction inwhich the water is circulated.

The leakage detecting device 13 can detect a pressure at a point betweenthe pump 7 and the valve 8 a in the water circuit 10 to reliably detectthe leakage of the refrigerant, irrespective of the position of the pump7.

Embodiments 1 and 2 have been described with respect to theair-conditioning apparatus as an example of the heat pump apparatus. Theair-conditioning apparatus is not limited to a room air-conditioningapparatus in which the amount of refrigerant is relatively small and mayinclude a large air-conditioning apparatus, such as a packageair-conditioning apparatus for business use or a multi-air-conditioningapparatus for a building. The heat pump apparatus is not limited to anair-conditioning apparatus and may be, for example, a chiller or acooler. In this case, instead of water, brine has to be used as a fluidfor the secondary circuit. Furthermore, the four-way valve is not neededbecause the apparatus is used only for refrigeration or cooling in thiscase.

REFERENCE SIGNS LIST

-   1 compressor, 2 four-way valve, 3 heat exchanger, 4 expansion valve,    5 intermediate heat exchanger, 6 refrigerant circuit, 7 pump, 8    valve, 9 heat exchanger, 10 water circuit, 11, 12 fan, 13 leakage    detecting device, 14 controller, 15 outdoor unit, 16 indoor unit, 51    plate, 52, 53, 54, 55 connection port, 56 refrigerant passage, 57    water passage, 58 area where a gas refrigerant tends to accumulate,    100 air-conditioning apparatus

1. A heat pump apparatus comprising: a first refrigerant circuit throughwhich a refrigerant is circulated, the first refrigerant circuitincluding a first compressor, a first heat source heat exchanger, afirst expansion mechanism, and a first intermediate heat exchangersequentially connected in loop by pipes; a fluid circuit through which afluid is circulated, the fluid circuit including the first intermediateheat exchanger, a first valve, a load heat exchanger, and a second valvesequentially connected in loop by pipes; a leakage detecting device thatdetects leakage of the refrigerant, circulated through the firstrefrigerant circuit, from the first intermediate heat exchanger into thefluid circuit; and a controller that closes the first valve and thesecond valve included in the fluid circuit when the leakage detectingdevice detects the leakage of the refrigerant, wherein the leakagedetecting device detects the leakage of refrigerant by detectingpressure within the fluid circuit.
 2. The heat pump apparatus of claim1, further comprising: a first casing that accommodates the firstcompressor, the first heat source heat exchanger, the first expansionmechanism, the first intermediate heat exchanger, the first valve, andthe second valve; and a second casing that accommodates the load heatexchanger.
 3. The heat pump apparatus of claim 1, wherein therefrigerant circulated through the first refrigerant circuit isflammable, and wherein the fluid circulated through the fluid circuit isnonflammable.
 4. The heat pump apparatus of claim 1, wherein when theleakage detecting device detects the leakage of the refrigerant, thecontroller stops the first compressor.
 5. The heat pump apparatus ofclaim 1, wherein the fluid circuit further includes a pump thatcirculates the fluid in such a manner that the fluid flows through thefirst intermediate heat exchanger, the first valve, the load heatexchanger, and the second valve in that order and the pump is connectedbetween the second valve and the first valve in a direction in which thefluid is circulated, wherein the first valve has an opening degree thatis controlled in such a manner that the fluid circulated through thefluid circuit flows at a predetermined flow rate, and wherein theleakage detecting device detects the leakage of the refrigerant bydetecting a pressure at a point between the pump and the first valve inthe fluid circuit.
 6. The heat pump apparatus of claim 1, wherein thefirst intermediate heat exchanger is placed in such a manner that aconnection port for the pipe connected to the first compressor isdisposed in upper part of the first intermediate heat exchanger and aconnection port for the pipe connected to the first expansion mechanismis disposed in lower part thereof.
 7. The heat pump apparatus of claim6, wherein the first intermediate heat exchanger is a plate heatexchanger including a plurality of plates stacked on one another and aplate at one end of the stacked plates has the connection port for thepipe connected to the first compressor and the connection port for thepipe connected to the first expansion mechanism, and wherein the firstintermediate heat exchanger is inclined in such a manner that theconnection port for the pipe connected to the first compressor facesobliquely upward.
 8. The heat pump apparatus of claim 7, wherein thefirst intermediate heat exchanger is the plate heat exchanger in whichthe connection port for the pipe connected to the first compressor isdisposed in a plate at an end of the plurality of plates another thanone end at which the plate having the connection port for the pipeconnected to the first expansion mechanism is disposed, and wherein thefirst intermediate heat exchanger is inclined in such a manner that theconnection port for the pipe connected to the first compressor facesobliquely upward and the connection port for the pipe connected to thefirst expansion mechanism faces obliquely downward.
 9. The heat pumpapparatus of claim 1, further comprising: a second refrigerant circuitthrough which the refrigerant is circulated, the second refrigerantcircuit including a second compressor, a second heat source heatexchanger, a second expansion mechanism, and a second intermediate heatexchanger sequentially connected in loop by pipes, wherein the secondintermediate heat exchanger is connected between the first intermediateheat exchanger and the first valve in the fluid circuit, wherein theleakage detecting device detects leakage of the refrigerant circulatedthrough the first refrigerant circuit and the refrigerant circulatedthrough the second refrigerant circuit from the first intermediate heatexchanger into the fluid circuit.
 10. The heat pump apparatus of claim9, wherein the refrigerant circulated through the first and secondrefrigerant circuits is R32 or a refrigerant mixture containing R32,wherein each of the first and second intermediate heat exchangers is aplate heat exchanger including a plurality of plates stacked on oneanother, and wherein each of the first and second intermediate heatexchangers is vertically placed in such a manner that the connectionports for the pipes are positioned on an upper side and a lower side ina vertical direction, and the first and second intermediate heatexchangers are arranged side by side horizontally.
 11. The heat pumpapparatus of claim 9, further comprising: a fan that generates airflowto deliver air which has exchanged heat with the refrigerant in one ofthe first and second heat source heat exchangers to the other one of thefirst and second heat source heat exchangers and allow the delivered airto exchange heat with the refrigerant in the other heat source heatexchanger.
 12. The heat pump apparatus of claim 2, wherein the heat pumpapparatus is an air-conditioning apparatus that conditions air in aroom, wherein the first casing is an outdoor unit installed outside theroom, and wherein the second casing is an indoor unit installed insidethe room.
 13. A method of controlling a heat pump apparatus including afirst refrigerant circuit through which a refrigerant is circulated andthat includes a first compressor, a first heat source heat exchanger, afirst expansion mechanism, and a first intermediate heat exchangersequentially connected in loop by pipes and a fluid circuit throughwhich a fluid is circulated and that includes the first intermediateheat exchanger, a first valve, a load heat exchanger, and a second valvesequentially connected in loop by pipes, the method comprising: aleakage detecting step of detecting, by a leakage detecting device,leakage of the refrigerant circulated through the first refrigerantcircuit from the first intermediate heat exchanger into the fluidcircuit based on pressure within the fluid circuit; and a valve controlstep of closing, by a controller, the first valve and the second valveincluded in the fluid circuit when the leakage detecting device detectsthe leakage of the refrigerant.